Layer 4 Protocol Decode

This is a transcript of a home-made sheet of ISO Transport protocol Decodes I prepared when decoding ISO Transport Protocol was a daily occupation. This was not recently :-) Putting it here allows me to throw the page away from my diary and might be of some interest. Check against the standard before you believe it.

ISO Transport Protocol Decodes

Transport Protocol
Name Type Valid
Parameters Max User Data
Connect Request CR All 128 C0-C7, 85-89, 8B 33 octets, not class 0 or 1
Connect Confirm CC All undef C0-C7, 85-89 33 octets, not class 0 or 1
Disconnect Request DR All 128 or
TPDU size
E0, C3 65 octets, not class 0 or 1
Disconnect Confirm DC not 0 undef C3 none
Data DT All TPDU size C3 TSDU
Expedited Data ED NF undef C3 exp TSDU (1-16 octets)
Acknowledge AK NC undef C3, 8A, 8C none
Expedited Ack EA NF undef C3 none
Reject RJ 1,3 undef none none
Error ER All undef C3, A1 none

NF: not class 0, not class 2 when non-explicit flow-control selected.
NC: as NF plus not class 1 when receipt confirmation selected.

TPDU formats

The following codes are used:

Error Codes (ER Reason)

Disconnect Codes (DR Reason)

Parameter Codes

Parameters appear as TLD (Type-Length-Data) triples.

TPDU Parameter Codes
Code Name Classes Length Value
85 Ack Time 4 2 binary integer: max ack time in ms
86 Resid. error rate not 0 3 oct 1: target as power of 10;
oct 2: min acceptable as power of 10;
oct 3: TSDU size as power of 2
87 Prority not 0 2 Integer, 0 is highest
88 Transit delay not 0 8 oct 1&2: target calling-called
oct 3&4: max acceptable calling-called
oct 5&6: target called-calling
oct 7&8: max acceptable called-calling
89 Throughput not 0 12 or 24 oct 1-12: max throughput;
oct 13-24: av throughput (optional)
1st 3 oct: target calling-called
2nd 3 oct: min acceptable calling-called
3rd 3 oct: target called-calling
4th 3 oct: min acceptable called-calling
8A Subsequence Num 4 2 sub-sequnce num for AK TPDUs
8B Ressign Time 1 or 3 2 TTR time in seconds in binary
8C Flow Control Conf 4 8 if b8 oct 1=1 next 31b are YR-TPDU-NR from rcd AK TPDU, next 16b sub-seq param of rcd AK TPDU, last 16b your credit.
Normal form: final bits of each field significant
A1 Invalid TPDU All undef bit pattern of RJ'd TPDU up to and including octet causing RJ
C0 TPDU size All 1 max TPDU as 2^value
default 07 (128 octets)
C1 Calling TSAP All undef id
C2 Called TSAP All undef id
C3 Checksum 4 2 Checksum
C4 Version not 0 1 01
C5 Security not 0 undef undef
C6 Additional Option not 0 1 default 01
b4=1 use network exp in class 1 else not
b3=1 use rcpt confirm in class 1 else not
b2=1 do not use checksums in class 4
b1=1 use transport expedited. b8-b5 0.
C7 Alt. protocol class not 0 n seq of single octets for alt prot classes
E0 Disconnect info All undef user-defined

Example TPDUs

These are examples from real connections, so might or might not be valid!
14D00089005D40C202D9C5C0010AC60103850205D0 is a CC with parameters for Called TSAP, TPDU Size, Additional Options, Ack Time 0680006D009800 is a DR with no reason specified

This page is maintained by Martin Ansdell-Smith
Last modified $Date: 2006/07/12 11:48:10 $.